Method and apparatus for continuously measuring the permeability of a porous layer



June 23, 1964 D. JORRE 3,138,014

METHOD AND APPARATUS FOR CONTINUOUSLY MEASURING THE PERMEABILITY OF A POROUS LAYER Filed Feb 19, 1963 United States Patent 3,138,014 METHOD AND APPARATUS FOR CQNTMUOUSLY MEASURING THE PERMEABILITY (IF A PU- RUUS LAYER Daniel Jorre, Scy-Eas (Moselle), France, assignor to Institut de Recherches de la Siderurgie Francaise, Saint Germain-en-Laye, France, a professional institution governed by the French law Filed Feb. 19, 1963, Ser. No. 259,633 Claims priority, application France Feb. 22, 1962 5 Claims. (Cl. 7338) The present invention relates to a system for continuously measuring the permeability of a moving porous layer, for instance a particulate material to be sintered.

It is current practice in the industrial sintering of ores on endless conveyors, such as continuous bands or chains, to control the speed of the conveyor in dependence on the permeability of the material to be sintered. In such installations, the moving conveyor carrying the material passes over a series of suction boxes and the conveyor speed is properly adjusted when a certain optimum distribution of the temperature of the gases drawn in by the suction boxes is obtained, such distribution depending on a maximum (peak) temperature in the last suction box but one. If the permeability of the sintering mixture or charge increases, the sintering reaction will proceed more quickly and the flame front will more rapidly reach the outer zone of the material to be sintered, since the air flow is solely controlled by the fan suction which is substantially constant. In such conditions, the temperature distribution observed in the suction boxes will differ from the optimum. Higher than ordinary temperatures are observed in the boxes in front of the penultimate box and the peak temperature is not attained in that box but in an earlier one.

In industrial practice, it is usual to increase the speed of the conveyor band or chain to allow for the increased permeability of the material being sintered and if the permeability of the material diminishes, the speed of the band or chain is reduced.

Such practices have the drawback that action can only be taken after a brief delay of, say, some minutes from the time a deviation is discovered.

The primary object of the present invention is to enable continuous measurement of the permeability of a sintering mixture and detection of its variations with a sufficiently quick response to enable the speed of the sintering conveyor band or chain to be regulated according to the measured permeability value.

The above and other objects and advantages are accomplished in accordance with this invention by supporting one surface of a porous layer of material being sintered on one surface of a permeable moving support and applying suction to the other surface of the permeable support, as conventional, but passing the moving support with the porous layer through a measuring station. The other surface of the porous layer is isolated at the measuring station without causing any substantial disturbance of the flow conditions of air passing to the other surface and a quantity of air equal to what would be supplied by the surrounding atmosphere is supplied to the isolated surface. The volume of supplied air is measured to determine the permeability.

The isolated surface section is produced by enclosing a volume of air at the measuring station above the other surface of the porous layer. A variable quantity of air is then supplied to the enclosed volume of air and air flow disturbances are eliminated by guiding the supplied air substantially evenly and uniformly through the enclosed volume of air to the other porous layer surface. The supplied quantity of air is adjusted to maintain the static pressure prevailing within the enclosed volume of air substantially equal to the atmospheric pressure surrounding the enclosed volume of air in a plane parallel to the support.

A slight air gap is maintained between the enclosed volume of air and the surrounding atmosphere, and the air pressure within the enclosed volume of air and in the surrounding atmosphere in this plane is measured continuously.

The preferred apparatus of the invention comprises a permeable movable support and suction means arranged to apply suction to one of its surfaces. A hood is supported above the outer surface of the porous layer of material being sintered and the hood has a rim slightly spaced from the layer surface to be out of contact therewith. Conduit means introduces a quantity of air into the hood and means is arranged in the conduit means for varying the quantity of air. Differential pressure gage means is arranged to measure the pressure differential within and outside the hood at the indicated plane and means is provided for controlling the air quantity varying means to introduce a quantity of air into the hood which maintains the pressure differential at the rim of the hood substantially at zero. Means is mounted preferably in the conduit means for measuring the supplied quantity of air.

The above and other objects, advantages and features of the present invention will be more fully explained in the following detailed description of a specific embodiment thereof, taken in conjunction with the accompanying schematic drawing showing a side view of the apparatus, partly in section.

Referring now to the drawing, the invention is illustrated in connection with conventional apparatus for sintering metal particles, such as iron ore, to form a porous bed of agglomerated ore, usually called bedding. The particulate material to be sintered is formed into a porous layer 2 carried by one surface of a moving permeable support 1. This support may be a foraminous endless band, grid or grating and is shown to carry a protective porous layer 3, for instance of a previously sintered iron ore layer. As conventional, this protective layer prevents the sintering flame from searing the moving support. Also in the conventional manner, suction boxes are arranged below the permeable support 1 to apply suction to the other surface of the support, one such suction means being shown at 4. Suitable draft means, such as fans, not shown, are arranged in communication with the suction boxes to maintain a sub-atmospheric pressure in the suction boxes.

According to the present invention, a hood 5 is supported above the porous layer 2, one of Whose surfaces is carried by the support 1 while the other surface is slightly spaced from the rim 5a of the hood. In the preferred embodiment shown herein, the hood has an axis and wall substantially perpendicular to the plane of the support and comprises air guide means 9 for producing a non-turbulent air flow through the hood. The hood may be, for instance, cylindrical or prismatic.

The illustrated suction box 4 and hood 5 define a measuring station through which the moving support 1 with the porous layer 2 pass While suction is applied to the other surface of the permeable support and a quantity of air is supplied to the other surface of the porous layer through hood 5. As clearly shown in the drawing, the hood isolates the other surface of the porous layer at the measuring station without causing any substantial disturbance of the flow conditions of air passing through the other porous layer surface.

a means constituted in the illustrated embodiment by a butterfly flap valve 8 is arranged in duct 6 for varying the quantity of air whereby a variable air quantity may be supplied to the isolated surface of the porous layer 2.

The illustrated air guide means in the hood consists of a plurality of guide vanes or bafies 9 which intersect and provide a plurality of uniform and parallel air flow channels. In this manner, the air will flow evenly and uniformly through the hood to the porous layer without causing any substantial disturbance of the flow conditions of air passing to and through the porous layer.

Means is provided for supplying to the isolated surface of the porous layer at the measuring station a quantity of air equal to what would be supplied thereto by the surrounding atmosphere normally and in the absence of the hood. This is done by adjusting the supplied quantity of air to maintain the static pressure prevailing within the hood substantially equal to the atmospheric pressure surrounding the hood in a plane parallel to the support. This means includes a diiferential pressure gage means arranged to measure the pressure differential within and outside the hood at this plane which, in the illustrated embodiment, is near the rim a of the hood.

The differential pressure gage means comprises, for instance, a conventional differential pressure gage 10 with movable pressure probes 11a and 11b connected to the gage 10 to transmit to this gage the air pressure which the outer ends of the probes receive from the surrounding atmosphere. As shown, the outer ends of the probes 11a, 11b are at the same level, i.e. in a plane parallel to the moving support or the porous layer, one extending into the hood and the other one extending to the atmosphere surrounding the hood. The two probes are identically curved and of like cross section to eliminate any dynamic effects due to the air flow velocity.

The gage 10 supplies a variable air pressure to any conventional type of pneumatic governor 12, an air conduit 17 connecting the gage 10 with one chamber of governor 12 and compressed air being supplied to the other chamber of the governor through air conduit 13, the two chambers of the governor being separated by a movable diaphragm, as well known.

In the described embodiment the gage 10 and pneumatic governor 12 are well known Bailey apparatuses B1-35, class AP, with a Bailey integral relay 1A. The butterfly flap valve 8 comprises a pneumatic auxiliary motor Bailey A744. According to the indications of the differential pressure gage 10, governor 12 will produce a corresponding control air pressure in conduit 16 which is connected to butterfly flap valve 8 and will so move the valve flap that the pressure difference between the air within and without the hood, as transmitted to the gage It by the outer ends of probes 11a, 11b, is always maintained at zero or within the order of a few tenths or hundredths of a millimeter Water column, which is practically zero for the purposes of this invention. Thus, the pressure gage 10 and pneumatic governor 12 constitute means for controlling the quantity of air introduced into the hood so that the pressure differential at the rim of the hood remains substantially at zero. This will prevent any substantial leakage of air between the surrounding atmosphere and the interior of the hood 5 through the air gap formed by the slight spacing between rim 5a of the hood and the surface of porous layer 2. Therefore, no laterial air flow will be produced at the bottom of the hood and the only effective flow of air extends in a direction perpendicular to the porous layer surface as though no hood were provided at the measuring station and the porous layer received air from the open atmosphere.

The permeability of the porous layer being a function of the quantity of air supplied to, and passing through, the layer, any conventional means may be provided for measuring the quantity of supplied air. In the illustrated embodiment, this includes a Venturi nozzle 14 and a flowmeter 15 corrected for pressure variations. This flowmeter 15 comprises a transmitter of differential pressure Honeywell 237-N1-C2 with a scale from 0 to 250 mm. water, a Honeywell transmitter of temperature with a scale from 0 to C. and Honeywell Sorteberg bridges C and A. These apparatuses are connected together in the way shown by the manufacturer in his technical booklets. If desired and in a manner well known, the indications of flowmeter 15 may be used to control the speed of the moving support 1 so that the support may move faster if the permeability surpasses a set limit to effect slower sintering or more slowly if the permeability is less than the set limit to increase the sintering time. Alternatively, the flowmeter output may be used to vary the moisture content of the particulate material to be sintered whereby the permeability may also be controlled.

It will be appreciated that the air flow through any given cross-section of the porous layer will depend on the pressure drop existing between the suction applied to one of its surfaces and the atmosphere in contact with its other surface on the one hand, and on the permeability of the layer, on the other hand.

The pressure drop between the suction boxes and the atmosphere depends in the first instance on the suction fans. In any given installation, this value is generally constant and invariable.

This air flow is thus directly and uniquely a function of the permeability of the layer and the measure of the air flow is thus a measure of the permeability. It is possible, therefore, to adjust the speed of the support according to this measured permeability of the material to be sintered. This has the advantage of enabling correcting action to be initiated much more rapidly than if only the temperatures in the last suction boxes are considered. It is necessary, consequently, to find a position on the moving support where the measured permeability is most typical or characteristic, in view of the variations in permeability along the support.

In fact, for each chain there is a region where permeability is practically constant. Such a region which may be found experimentally is located in the middle portion of the chain. For example, in a chain having 18 suction boxes, there are only slight variations in permeability from the 4th or 5th box down to the 10th box. In that case the 4th or 5th box would be selected as a location for measuring operation, in order that the variations in permeability be detected as soon as possible.

In order to measure the flow volume passing through any given section of the porous layer, without disturbing the airflow conditions above the layer, a particular sec tion of the latter is isolated and the exact quantity of air which would normally pass through this section is supplied to the isolated section through a duct in which the true flow volume is measurable by any suitable means.

This measurable air flow is discharged onto the surface of the porous layer through. the above-described hood which incorporates guide vanes directing the air parallel to the axis of the hood and ensuring a non-turbulent air flow. An air gap is left between the base of the hood and the surface of the porous layer. This gap has crosssection permitting air flow towards the inside or the outside of the hood if a pressure differential exists therebetween. This flow should be practically nil for ordinary pressure and flow conditions at the isolated surface of the porous layer. The presence of an air leak through this gap will, in fact, be associated with the existence of a pressure ditference or gradient between the inside and the outside of the casing. The measure of this pressure differential, and its cancellation by influencing the air volume introduced into the hood, will enable normal flow conditions to be maintained through the porous layer, in the direction perpendicular to the hood.

While the invention has been described in connection with a specific embodiment, it will be clearly understood that many variations and modifications may occur to those skilled in the art without departing from the spirit and scope of this invention as defined in the appended claims.

What is claimed is:

l. A method of continuously measuring the permeability of a porous layer of material, comprising the steps of supportnig one surface of the porous layer on one surface of a permeable moving support, passing the moving support with the porous layer through a measuring station, applying suction to the other surface of the permeable support at the measuring station, isolating the other surface of the porous layer at the measuring station Without causing any substantial disturbance of the flow conditions of air passing to the other surface, supplying to the isolated surface at the measuring station a quantity of air equal to What would be supplied by the surrounding atmosphere and measuring the volume of the supplied air.

2. A method of continuously measuring the permeability of a porous layer of material, comprising the steps of supporting one surface of the porous layer on one surface of a permeable moving support, passing the moving support with the porous layer through a measuring station, applying suction to the other surface of the permeable support at the measuring station, enclosing a volume of air at said measuring station above the other surface of the porous layer, supplying a variable quantity of air to said enclosed volume of air, guiding the air substantially evenly and uniformly through said enclosed air to said other surface adjusting the supplied quantity of air to maintain the static pressure prevailing within the enclosed volume of air substantially equal to the atmospheric pressure surrounding the enclosed volume of air and measuring the volume of the supplied air.

3. The method of claim 2, further comprising the steps of maintaining a slight air gap between the enclosed volume of air and the surrounding atmosphere, and continuously measuring the air pressure within the enclosed volume of air and in the surrounding atmosphere in said plane.

4. An apparatus for continuously measuring the permeability of a porous layer of material, comprising (a) a permeable moving support, one surface of the porous layer being carried by one surface of the permeable support;

(b) a suction means arranged to apply suction to the other surface of the permeable support;

(c) a hood supported above the other surface of the porous layer and having a rim slightly spaced from the other surface;

(:1) conduit means introducing a quantity of air into the hood;

(e) means arranged in the conduit means for varying the quantity of air;

(7) differential pressure gage means arranged to measure the pressure differential within and outside the hood;

(g) means for controlling the air quantity varying means to introduce a quantity of air into the hood which maintains the pressure differential at the rim of the hood substantially at zero; and

(h) means for measuring said quantity of air.

5. The apparatus of claim 4, wherein the hood has an axis and Wall substantially perpendicular to the said 30 plane and further comprising air guide means arranged in the hood for producing a non-turbulent air flow through the hood.

No references cited. 

1. A METHOD OF CONTINUOUSLY MEASURING THE PERMEABILITY OF A POROUS LAYER OF MATERIAL, COMPRISING THE STEPS OF SUPPORTING ONE SURFACE OF THE POROUS LAYER ON ONE SURFACE OF A PERMEABLE MOVING SUPPORT, PASSING THE MOVING SUPPORT WITH THE POROUS LAYER THROUGH A MEASURING STATION, APPLYING SUCTION TO THE OTHER SURFACE OF THE PERMEABLE SUPPORT OF THE POROUS LAYER AT THE MEASURING STATION WITHOUT CAUSING ANY SUBSTANTIAL DISTURBANCE OF THE FLOW CONDITIONS OF AIR PASSING TO THE OTHER SURFACE, SUPPLYING 